December 09, 2010

Persian gulf oasis hypothesis

A once fertile landmass now submerged beneath the Persian Gulf may have been home to some of the earliest human populations outside Africa, according to an article published today in Current Anthropology.

Jeffrey Rose, an archaeologist and researcher with the University of Birmingham in the U.K., says that the area in and around this "Persian Gulf Oasis" may have been host to humans for over 100,000 years before it was swallowed up by the Indian Ocean around 8,000 years ago. Rose's hypothesis introduces a "new and substantial cast of characters" to the human history of the Near East, and suggests that humans may have established permanent settlements in the region thousands of years before current migration models suppose.

In recent years, archaeologists have turned up evidence of a wave of human settlements along the shores of the Gulf dating to about 7,500 years ago. "Where before there had been but a handful of scattered hunting camps, suddenly, over 60 new archaeological sites appear virtually overnight," Rose said. "These settlements boast well-built, permanent stone houses, long-distance trade networks, elaborately decorated pottery, domesticated animals, and even evidence for one of the oldest boats in the world."

But how could such highly developed settlements pop up so quickly, with no precursor populations to be found in the archaeological record? Rose believes that evidence of those preceding populations is missing because it's under the Gulf.

"Perhaps it is no coincidence that the founding of such remarkably well developed communities along the shoreline corresponds with the flooding of the Persian Gulf basin around 8,000 years ago," Rose said. "These new colonists may have come from the heart of the Gulf, displaced by rising water levels that plunged the once fertile landscape beneath the waters of the Indian Ocean."

Historical sea level data show that, prior to the flood, the Gulf basin would have been above water beginning about 75,000 years ago. And it would have been an ideal refuge from the harsh deserts surrounding it, with fresh water supplied by the Tigris, Euphrates, Karun, and Wadi Baton Rivers, as well as by underground springs. When conditions were at their driest in the surrounding hinterlands, the Gulf Oasis would have been at its largest in terms of exposed land area. At its peak, the exposed basin would have been about the size of Great Britain, Rose says.

Evidence is also emerging that modern humans could have been in the region even before the oasis was above water. Recently discovered archaeological sites in Yemen and Oman have yielded a stone tool style that is distinct from the East African tradition. That raises the possibility that humans were established on the southern part of the Arabian Peninsula beginning as far back as 100,000 years ago or more, Rose says. That is far earlier than the estimates generated by several recent migration models, which place the first successful migration into Arabia between 50,000 and 70,000 years ago.

The Gulf Oasis would have been available to these early migrants, and would have provided "a sanctuary throughout the Ice Ages when much of the region was rendered uninhabitable due to hyperaridity," Rose said. "The presence of human groups in the oasis fundamentally alters our understanding of human emergence and cultural evolution in the ancient Near East."

It also hints that vital pieces of the human evolutionary puzzle may be hidden in the depths of the Persian Gulf.

Current Anthropology, 51:849–883, December 2010 DOI: 10.1086/657397

New Light on Human Prehistory in the Arabo-Persian Gulf Oasis

Jeffrey I. Rose

The emerging picture of prehistoric Arabia suggests that early modern humans were able to survive periodic hyperarid oscillations by contracting into environmental refugia around the coastal margins of the peninsula. This paper reviews new paleoenvironmental, archaeological, and genetic evidence from the Arabian Peninsula and southern Iran to explore the possibility of a demographic refugium dubbed the “Gulf Oasis,” which is posited to have been a vitally significant zone for populations residing in southwest Asia during the Late Pleistocene and Early Holocene. These data are used to assess the role of this large oasis, which, before being submerged beneath the waters of the Indian Ocean, was well watered by the Tigris, Euphrates, Karun, and Wadi Batin rivers as well as subterranean aquifers flowing beneath the Arabian subcontinent. Inverse to the amount of annual precipitation falling across the interior, reduced sea levels periodically exposed large portions of the Arabo-Persian Gulf, equal at times to the size of Great Britain. Therefore, when the hinterlands were desiccated, populations could have contracted into the Gulf Oasis to exploit its freshwater springs and rivers. This dynamic relationship between environmental amelioration/desiccation and marine transgression/regression is thought to have driven demographic exchange into and out of this zone over the course of the Late Pleistocene and Early Holocene, as well as having played an important role in shaping the cultural evolution of local human populations during that interval.

14 comments:

"Therefore, when the hinterlands were desiccated, populations could have contracted into the Gulf Oasis to exploit its freshwater springs and rivers".

Presumably if sea level fell enough the Gulf would have become a fresh water lake. This makes more sense than:

"early modern humans were able to survive periodic hyperarid oscillations by contracting into environmental refugia around the coastal margins of the peninsula".

If the climate was so hyperarid there would be very few fresh water streams emptying into the coastal margins. Coastal habitat is not very productive for humans if they don't have access to fresh water.

"Presumably if sea level fell enough the Gulf would have become a fresh water lake"

There could be some small fresh water bodies of water, but the Persian Gulf generally is pretty flat and pretty evenly grades down towards the Indian Ocean. For a fresh water lake you need a basin and it needs to be fed by an outside source and drain to someplace else. Lakes that don't drain to the sea (e.g. the Great Salt Lake and the Dead Sea) tend to increase in salinity over time.

"If the climate was so hyperarid there would be very few fresh water streams emptying into the coastal margins."

Not so. For example, most of the Colorado River basin is hyper arid, but it includes many fresh water streams that empty into coastal areas. Similarly, the Tigris, Eurphrates, Nile and Niger Rivers are all healthy fresh water rivers that empty into coastal areas yet are surrounded by hyperarid environments. Australia also has fresh water rivers that flow through hyperarid environments.

A hyperarid climate can be localized. Fresh water river flow depends mostly on precipitation and snow melt at their often distant mountain sources, and glacial melt can feed rivers for long periods of time even when mountain precipitation is only intermittent. Ground water reservoirs that produce oasis springs in deserts can also persist for very long periods of time until tapped.

Also, consider that for the bulk of the hypothetical "Gulf Oasis" period that we are talking about population densities associated with people who have neither domesticated crops nor domesticated animals. Even if a river is reduced to a pretty feeble creek for some of the year, availability of animals to hunt and plants to gather, rather than fresh water supplies, are going to be the limiting factor.

On the merits the paper makes a circumstantial case, but has almost no direct evidence. The Neolithic Revolution can explain a burst in settlement without an oasis hypothesis because it made food available were it wasn't in a hunter-gatherer mode. Surely some hominin traces are beneath the Persian Gulf, but in the period from ca. 50,000 to 75,000 years ago when modern humans disappeared in the Levant, one would expect Neanderthals, not Cro-Magnons in the Gulf, rather than a refugia of Cro-Magnons, in the absence of archeological evidence to the contrary.

That woman, sorry I cannot remember her name, proposed that the humans that left Africa had used the route across the Red Sea when sea levels were very low to cross over to nearby Asia and sojourned there for some time. The region where the first humans hunted and gathered is now under the Indian Ocean, but then was a land filled with many fresh water springs and oases. Fresh water is still supposedly being released from those springs under the Indian Ocean off the Arabian Coast.

Maybe there is something in that hypothesis, but some more proof is needed as in dredging the offshore areas off South Arabia to find some tools, artifacts and maybe human bones. Obviously the land sites in the now and then desiccated Arabia isn't going to give that much proof.

I lived in the region and speak/read Arabic and have long been fascinated by Dilmun, which the present island of Bahrain is part of. There are around 40,000 unexcavated grave mounds on Bahrain which have excited much interest by archeologists put off by the climate and politics of the region.

The Sumerian civilization always said that it originated 'from the sea' which fits nicely into this thesis. Indeed, the geologists at ARAMCO in Saudi Arabia explained to me while I was at the Embassy there that the drowned mouth of the Tigris and Euphrates had once had a delta near the Straits of Hormuz between Iran and Oman, with the entire Garden of Eden, according to local Arab lore, once existing in the region. Indeed, in Jeddah, the burial place of Eve was venerated and in Arabic language, Yemen is a word meaning "right" and Shammal meaning left, perhaps a reference to eastward-facing sun worshipers at dawn in the millennia long before the Christian era.

On the merits the paper makes a circumstantial case, but has almost no direct evidence. ... Surely some hominin traces are beneath the Persian Gulf, but in the period from ca. 50,000 to 75,000 years ago when modern humans disappeared in the Levant, one would expect Neanderthals, not Cro-Magnons in the Gulf, rather than a refugia of Cro-Magnons, in the absence of archeological evidence to the contrary.

Well, there are a couple of groups of researchers that strongly disagree with you - although, as everywhere, actual skeletal remnants would be highly desired:

These too links appear to be the same study. This study reports finds of pre-Archelean, Acheulean and Mousterian artifacts in Arabia. The former two imply Homo Erectus. The latter imply Neanderthals, neither is good proof of an ancestral modern human presence. The study expressly states that "Obviously, theBarakah assemblage lacks any . . . ‘Upper Paleolithic’ elements."

http://www.sciencemag.org/content/326/5950/224.full.pdf

The punch line in this one is "stone tools found in Arabia and India suggest that Homo sapiens may have made its way out of Africa much earlier than 50,000 years ago, as usually assumed."

In India, I agree. Homo sapiens were there probably pre-Toba. The evidence in Arabia is pretty thin and the researches in that study, like the one cited in the original post, decidely hedge their bets. Obviously, new finds could provide direct evidence that is absent now. But, the direct evidence, if it exists, should be underwater in the Persian Gulf and not far off the Arabian coast, and I don't know of any under water archeological finds in these places, although I'd love to know more.

http://www.springerlink.com/content/t31615361u045k59/

The abstract and pre-view page doesn't shed much light on whether this is continuity or discontinuity in Arabia at the Pleistocene–Holocene divide (no one doubts that there were modern humans in Arabia in the Holocene and even in the last Upper Paleolithic). So, I can't comment on this link.

"the Persian Gulf generally is pretty flat and pretty evenly grades down towards the Indian Ocean. For a fresh water lake you need a basin and it needs to be fed by an outside source and drain to someplace else".

I was thinking that Hormuz may have closed at times of low sea level.

"Similarly, the Tigris, Eurphrates, Nile and Niger Rivers are all healthy fresh water rivers that empty into coastal areas yet are surrounded by hyperarid environments. Australia also has fresh water rivers that flow through hyperarid environments".

But the sources of those rivers is outside those hyperarid environments. Much of Arabia would not supply much fresh water during times of hyperaridity.

"in the period from ca. 50,000 to 75,000 years ago when modern humans disappeared in the Levant, one would expect Neanderthals, not Cro-Magnons in the Gulf"

Possibly so. But Neanderthals definitely seem cold-adapted so may have been confined to the mountainous regions to the north. And modern humans definitely seem to have emerged into the Levant by around 100,000 years ago.

"in the absence of archeological evidence to the contrary".

That's really what it comes down to.

"In India, I agree. Homo sapiens were there probably pre-Toba. The evidence in Arabia is pretty thin"

But they have to have moved to India by some route or other. Through Arabia seems a fairly obvious one.

"The abstract and pre-view page doesn't shed much light on whether this is continuity or discontinuity in Arabia at the Pleistocene–Holocene divide"

Discontinuity seems most likely to me. The spread of Y-hap J through Arabia looks to have been a movement into an uninhabited region, or largely so. I suppose it's possible that Y-hap E is an ancient survivor there, but it's generally considered to be a later OoA.

"Much of Arabia would not supply much fresh water during times of hyperaridity."

The source of the Persian Gulf drainage basin is mostly in the mountains of Turkey and Iran.

"Neanderthals definitely seem cold-adapted so may have been confined to the mountainous regions to the north. And modern humans definitely seem to have emerged into the Levant by around 100,000 years ago."

Neanderthals were in the Levant before, during and after the period of anatomically modern human presence there from ca. 100,000 to 75,000 years ago. The climate of a Gulf Oasis was presumably not that different from that of the Levant. Indeed, even if the Gulf was not an AMH oasis, it may very well have been a Neanderthal refugia.

"Neanderthals were in the Levant before, during and after the period of anatomically modern human presence there from ca. 100,000 to 75,000 years ago".

Were they? I was certainly under the impression they didn't arrive there until around 70,000 years ago.

"The source of the Persian Gulf drainage basin is mostly in the mountains of Turkey and Iran".

Exactly as it is today.

"the Persian Gulf generally is pretty flat and pretty evenly grades down towards the Indian Ocean".

In which case the shoreline would simply recede down the gulf. The surrounding habitat would presumably also just retreat down the gulf giving rise to no substantial alteration of the habitat around the gulf. In times of increased aridity the habitat would be even less hospitable than it is today. For the 'Persian Gulf Oasis' hypothesis to have any validity something different must have been operating.

For Neanderthal dates prior to the earliest known anatomically modern human traces in the Levant see e.g. date for Tabun cave (100 kya to 300 kya +/-), and "The Zuttiyeh skull in Israel, ssociated with an early Middle Paleolithic industry of the Levant region, or eastern Mediterranean, called the Acheulo-Yabrudian. This industry at Zuttiyeh has been dated to as late as 148,000 years before the present (B.P.) (Bar-Yosef, 1998: table 1), but other estimates place the Zuttiyeh skull as early as 200,000 to 250,000 B.P. (Zeitoun, 2001: 522)." (affiliation disputed).

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